With the rapid development of wireless communication technology, reconfigurable intelligent surface (RIS) has been recognized
as a revolutionary technology for future wireless communication
systems [1]}.
An RIS consists of passively reflecting elements and each element can independently induce certain phase shift changes to the incoming signal [2]},[3]}.
RIS-aided communication systems have been extensively studied in [4]}, [5]}. The authors in [4]} investigated an RIS-assisted massive multiple-input multiple-output (MIMO) system, derived a closed-form expressions of the rate. In [5]}, the performance of RIS-assisted MIMO systems with direct links was studied based on statistical channel state information (CSI).
